1. Field of the Invention
The present invention relates to a resin composition comprising a polyester and a specified flameretarding agent containing an epoxy and a halogen. The present invention further relates to an electric wire covered with a polyester resin and more particularly to an electric wire covered with a resin composition used as a covering material, which does not suffer any flexibility loss due to heat history, has excellent flame retardancy and comprises a polymer comprised of an aromatic polyester as a main skeleton and a halogen compound containing an epoxy group incorporated therein.
2. Prior Art
Rubber, polyvinyl chloride, polyethylene, polypropylene, nylon, etc. have hitherto been used as a wire covering material. In particular, polyvinyl chloride has extensively been used for this application from the viewpoint of flame retardancy and mechanical strengths. In recent years, with an increase in the severity of the environment under which the above-described covering materials are used, requirements for the properties of the covering material including not only excellent thermal resistance and electrical characteristics but also flame retardancy and an excellent thin-wall forming property necessary for realizing space saving have been increased.
Although crosslinked polyethylene and fluororesin can meet the above-described requirements, they are unsatisfactory in that the former is poor in the thin-wall forming property and the fluororesin is expensive.
Attention has been paid to polyethylene terephthalate and polybutylene terephthalate because they are excellent in the thin-wall forming property as well as in the mechanical strengths (flexibility, abrasion resistance, etc.), thermal resistance, and electrical characteristics. However, these terephthalates are insufficient in the flame retardancy. Further, since they are crystalline resins, the heat history including heating treatment after covering a wire and heating during the use of the covered wire bring about a remarkable lowering in the flexibility thereof. This in turn brings about a lowering in the mechanical strengths such as impact resistance. For this reason, the terephthalates use in the vicinity of heat sources and in environments having a danger of heat buildup should be avoided, which more or less impose restrictions on the use of these materials.
In general, various flame retardant compositions prepared by incorporating various halogen-containing flame retardants in an aromatic polyester have hitherto been proposed. However, in the case in which such is used as a wire covering material, as in the present invention, it is very difficult to simultaneously satisfy various characteristics such as flame retardancy, frictional and abrasion resistance, and flexibility (flexing property and high percentage elongation), and to maintain, without causing any flexibility loss due to heat history even when exposed to a heating atmosphere for a long period of time, characteristics of initial high percentage elongation and flexing property.